Turbine rotors often experience cracking requiring repair before the end of their design life due to the environment associated with such turbines (e.g., high temperatures and/or pressures). For example, a rotor 10 (FIG. 1) may experience cracking in at least two locations at or before half of the design life thereof is consumed. Such cracking may occur at the bottom of an L-Groove cooling slot formed in the rotor and at a fabrication weld formed in bridge rails thereof. The bridge rails may support heat shields during operation of the turbine, which are mounted axially in openings between the bridge rails. Bottoms of the L-Grooves may experience cracking due to low cycle fatigue and poor geometry. High local mechanical stresses resulting from the original weld geometry of the bridge rails may cause premature low cycle fatigue cracking in the fabrication weld.
The cracks formed in such turbine rotors are conventionally repaired by machining an opening 300 in a circumferential portion 310 of the rotor which is the same width as a top end of an L-Groove 320 as depicted in FIG. 2. In particular, any cracks in circumferential portion 310 (e.g., in a fabrication weld thereof) or at a bottom end 321 of L-Groove 320 may be removed by machining through the opening created. After machining the cracks from groove 320, the groove may be closed by welding the opening shut. The location of a conventional weld does not allow a gentle transition between the weld and sidewalls 330 of the groove. Instead, a sharp angle is formed at an intersection 340 between a conventional weld 331 and adjacent side walls of the groove. Such an abrupt transition created by such a conventional weld increases stress in the area of the weld and allows for premature failure. Further, such a repair causes heat effected zones of the welds to be placed in such stressed areas.
Thus, a need exists for an improved method for repairing cracks in turbine rotors.